Wire line core barrel



April 8, 1958 Filed Aug. 14. 1955 F. PlcKARD ETAL 2,829,868

WIRE LINE CORE BARREL 2 Sheets-Sheet l IJWWWW v- To RNE Y6 April 8, 1958 A. F. PICKARD ET AL WIRE LINE CORE BARREL Filed Aug. 14. 1953 2 Sheets-Sheet 2 /47- TOR/VE YJ' wml: LINE Conn BARREL Albert Frank Pickard, Minneapolis, and Walter W. Svendsen, Si. Paul, Minn., assignorsto E. J. Longyear Company, Minneapolis, Minn., a corporation of Delaware Application August 14, 1953,'seria1 No. 374,204 11 claims. (c1.2ss72) This invention relates to the art of drilling deep wellsV for oil, gas, sulfur and the like and especially to drilling exploratory shafts for sampling subterranean formations in searching for mineral deposits and the like. More particularly, this invention relates to improvements in core drills having a tubular drill stem terminating in a bit for drilling cores the drilling apparatus being characterized by having a detachable retractable core barrel and means for removing the core barrel from `the core drill without the necessity of withdrawing the complete drill stem and bit from the hole. commonly known as wire line core drills and wire line core barrels since the core barrel portion is removed from the drill stem by use of a Wire line carrying a suitable grappling tool at its lower end. This invention relates as well to an improved grappling device.

In the past, core drills of this general type have been subject to certain disadvantages. One disadvantage has involved to use of complicated latch mechanisms to lock the removable core barrel assembly in operating position, whereby locking engagement or disengagement can occur automatically as the core barrel assembly is lowered into operating position or lifted by the wire line. These complicated latch mechanisms were subject to mechanical failure, breakage, erosion and wear due to drilling muds and the like.

It is an object of this invention to provide an improved wire line core barrel and it is an object to provide a core drill having a detachable retractable wire line core barrel with an improved simplified strengthened latching mechanism so as to prevent the core sample from pushing the core barrel upwardly through the drill stem and at the same time lock the portions of the core barrel in contact with the drill stemagainst rotation within the drill stem while allowing free relative rotation of the core receiving portion of the core barrel assembly.

Another disadvantage present in prior art core drills has been that the lower end of the core barrel has rested upon a shoulder or similar protuberance on the inside of the drill bit itself and thereby has been subject to damage upon coming to rest after dropping down through the length of the drill stem. This has tended not only to damage the lower end of the core barrel but also has resulted in damaging the core or in some cases in jammingl the core drill, rendering further drilling impossible.

lt is another object of this invention, therefore, to provide a core drill having `a detachable retractable wire line core barrel provided with means for bringing the core barrel to rest short of striking the core bit at the end of the drill stem and provided with means for by-passing the drilling iluids around thecore barrel supporting means. j

ln the past, considerable difficulty has been encountered in readily disengaging the core barrel from the core drill after it has received the desired core sample.

One of the objects of this invention is to provide a core drill having a retractable core barrel with means for readily and automatically releasing the core barrel Such devices are" 2,829,868 Patented FCC from the core drill andup through the lengthofthe drill stem.

A further object of this invention, therefore, is to provide improved means for easily and readily securely grappling the core barrel fordetaching it from Vthe core drill and retracting it through the drill stem.

Another diiliculty encountered in the past has been the tendency of the core barrel to cramp or bendwhere it is grasped by a grappling` tool when the grappling tool` core barrel assembly is withdrawn from the drill string at the surface. This is due to the pivoting allowed at the jaws of the grappling tool of prior devices. Occasionally in such prior devices, the entire core barrel would break loose and fall back to the bottom of the well, damaging both thecore barrel and the core sample.

It is another object of this'invention to provide a grappling tool or overshot assembly for retracting the loaded. core barrel through the drill string from the bottom of the well which is vprovided with means for stabilizing the core barrel and retracting assembly and substantially preventing cramping or bending movement between them. As the core barrel sample moves up into the core receiving tube of the core barrel inner tube assembly, the resultant forces cause the latching dogs of the assembly to become jammed so that they can be released only with difficulty. It is an object of the invention to provide an apparatus which obviates or reduces these diliculties. Y

It has also' sometimes occurred in the use of existing core barrel devices that for one reason or anothei the entire core barrel and grappling tool assembly becomes jammed at the bottom of the drill string but the operator working at the surface becomes apprised of this fact only when the wireline snaps and breaks. It then becomes necessary to withdraw the entire drill string in order to recover the core barrel andgrappling device and line.

Another object of this invention is to provide an overshot assembly which is part of this inventionv with a shearing pin coupling so `that in case of jamming of the core Vbarrel and grappling tool assembly .the pin will shear off rather than permitting the' wire line to4 break.

Other objects of this invention will become apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following Figures l and 2, taken together, constitute a longitudinal sectional view of a core drill, core barrel inner tube as-I sembly, and overshot assembly embodying the present` invention, Figure 1 showing theupper portion and Figure' 2 showing the lower portion.

Figure 3 is an enlarged transverse sectional View ofthe hanging support means and fluid by-pass channels of the core barrel assembly taken along the line and in the direction of the arrows 3 3 of Figure 2.

Figure 4, is an enlarged transverse view, partly insection, of the latching andgrapplingportions of the core4 barrel assembly of this inventiontaken generally along description setting forth in` the line and in the direction of the arrows 4-4 of Figure l.

Figure 5 is a longitudinal sectional view of the latch andlocking means. taken along theline and in the direction of the arrows 5-5 of Figure l. Referringnow to the drawings and particularly to Figures land 2, there is here illustrated one embodiment of invention comprising generally, a hollow drill tube 'made up of sections'of pipe or tubing screw threaded at their ends for coupling and having at their lower end abit-11. In -the art, the drill tubes, of which the lowermost end is shown in Figurel, are sometimes designated drill rod, drill string or drill stem. The term drill stem willV be used herein. The drill stem 10 is hollow and in it at its lower end is positioned a core barrel inner tube assembly generally designated 20, in which thecore isreceived. l

The lowermost section of the drill stem carries a'drill bit 11.and in the formhere illustrated is a so-called diamond core drill. -The cutting surfaces are formed by the annularA face 12 and sides 14 of the thickened bottom portionofthe bit which are formed of or surfaced with diamondsfembedded in a hard facing material. While the invention is illustrated by reference to a diamond core drill, itis to be understood, however, that the invention is not limitedthereto but on the contrary is applicableV to all types of hollow core bits such as are conventionally used in taking core samples. The drill bit portion 11 is threaded at 15 onto the reaming shell 21 which may have diamonds or other hard points on its outer surface. bit 11 has a widened bit face 12 having a maximum diameter 14 and inner (or minimum diameter) 16. An inner shoulder is formed at 17. The cuttingface 12 is provided with a central aperture or opening 1S through which the core sample, as it is cut, enters into the core barrel inner tube assembly indicated generally a-t 2i). The reaming shell 21 when provided on its outer surface with a cutting point such as diamonds embedded in a hard facing coatingserves to ream the hole to true diameter. The reaming shell is in turn mounted by screw threads on the outer tube 22 at the bottom of the drill stem. The core barrel inner tube assembly indicated generally at fits loosely within the outer tube 22 extending down to the drill bit 11, being provided with latch body shoulders 24 which face downwardly and are adapted to seat upon The an annular .internal shoulder 25 in a collar or hanger coupling 261 screwed onto upper end of the outer tube 22. The'lowercore-receiving end of the core barrel inner tube assembly 20is held' free from contact with the inner shoulder 17 of the drillbit.

The core barrel inner tube assembly 20 includes a latch body 44 (with its latches 55), latch release tube 66-69, and spindle 35,.cap 32, and core receiving tube 27', extension 28 therefor and all associated parts. The core receiving tube 27 has a replaceable core tube extension f 2 8 coupled to |its lower end and a core lifter 29 and a core lifter case 30 threaded onto the lowery end of the core tube extension 28. Case 30 holds the core lifter 29. The

core lifter 29 comprises a resilient split spring steel ringA having a plurality of longitudinal slots or ribs around its inner periphery which are adapted to grasp and hold the core sample, so as to break oi the core and then hold rt'from falling from the core barrel as the core barrel is being raised tothe surface. The lifter ring'29 is tapered on its' outerv surface and mates with the correspondingly tapered inner surface of core lifter case 3l). Hence as assembly 20 (tubes 27, 28 and 30) is lifted, the ring 29 1s contracted onto the core, untilthe core is pulled and breaks free. The lifting motion for this will be explained herein.

A threaded coupling member 31 which is a part of the core barrel inner vtube assembly 20,r joins the inner tube 27 to the inner tube cap member-'32. This coupling 31 1s provided with ports 34 to permit escape of drilling fluids asV the core lls up the core barrel inner'tllbe. An velm;-

gated spindle 35. of the core barrel inner tube assembly 20 is threaded at each end and is disposed in a central aperture 36 through the inner tube cap assembly 32. Fitted over the lower threaded end 37 of the spindle 35 are hanger washers 38 held in place 'oy a castellated nut 39 screwed onto the spindle and in turn held fixed by cottcr pin 40 extending through hole 41 through the spindle and resting in the slot of the nut. The upper threaded end of the spindle is screwed into a latch body 44 of the core barrel inner tube assembly 20.

Mounted on the spindle and held by dowel pins 42 to the latch body 44 and inner tube cap 32 respectively are a pair of wear' washers 45 and 46 and mounted on the spindle between the wear washers are a pair of ball, roller, or other anti-friction bearing assemblies 47 and 48 permitting vfree rotation of the entire core barrel assembly with respect to the latch body 44. Thus while Vthelatch body of the core barrel inner tube assembly 20 will rotate with the drill stem, the core receiving tube 27 and associated parts are freely journaled with respect to the latch body 44 and actually remain stationary and thus protect the core sample within the inner tube from damage due to rotation of the tube.

, The latch body 44 of the core barrel inner tube assembly 20 comprises a thickened lower portion provided with downwardly facing shoulders 24 for seating upon the inner annular upwardly facing shoulder 25 of hanger coupling 26. This seating of latch body 44 (shoulder 24) on shoulder 25 of coupling 26 of the drill stem provides an accurate bottom on which the core barrel inner tube assembly 20 seats when in drilling position. ln this position the lower end piece 39 (of the core receiving tubes 27-30) clears shoulder 1.7. Also when the core receiving tubes 27-30 are lled with Core and thc driller wants to pull the core, it must be broken free of its attachment with the earth formation thru which the drill is proceeding. Todo this, the driller lifts or pulls the drill stem 10 and this pulling force is transmitted from the drill stem 1t) via coupling 26, shoulders 24--25 to latch body 44 thence thru spindle 35, nut 39, washers 35 to cap 32 and thence thru coupling 31 and tubes 27 and 28 to end -piece 30, which, reacting upon the lifter ring 29, compresses it to grip and lift and break the core free, as aforesaid.

I A plurality of arcuate slots or channels 50 in the latch body 44 and adjacent the shoulders 24-25 provide passage for drilling fluids around the shoulders when the core barrel is seated in the hanger coupling 26. As best shown in Figures 4 and 5 the upper section 51 of the latch body 44 is of lesser diameter than the lower portion and is Vprovided with an elongated transverse slot 52 and with a hole 54 drilled through the latch body perpendicular to the elongated slot adjacent the lower end of the slot. Positionedqwithin the elongated slot 52 of the latch body are a pair of normally outwardly extending latching lugs or `dogs 55 in oi-set side-by-side relation and pivotally mounted bymeans of pin 57 passing through the perpendicular hole 54 in the latch body and through corresponding lholes in the lower ends of the dogs. Each of the latch dogs 5,5 is provided with an outer hardened tooth 58 (see Figure l) which extends through an opening 59 in the latch retractingcase 66 for engaging an inner annular latching hold-down shoulder 60 formed by the lower threaded end of locking coupling 61. Locking coupling 6l is screwed into guide coupling 62 and both are a part of drill stem 10'. The shoulder 60 reacting upon dogs 55 and hence uponl the latch body 44 prevents the inner core-receiving tube 27 from lifting while drilling. Each of the latch dogs 55 is also provided with a spring member 64 riveted tothe inner edge thereof for engagement with the inner wally of the latch retracting case 66 to urge thelatch dog normally outwardly for engagement with the shoulder of the drill stern. It is apparent that instead of beingriveted as shown the springs may also be fastened byuothermeans such as spot welding, nuts and bolts or thelike.A

Fitted loosely over and around the upper portion of the latch body and adapted to rest upon the shoulder 67 formed by the thickened lower section of the latch body is a tubular latch retracting case 66 open at the lower end and having an inner diameter such that it will slide on portion 51 of the latch bodyl 44. Case 66 has a threaded spear-head receiving opening 68 at the internally thickened upper end 69. The latch retracting case 66 is provided with slots 59 (see Figure 5) through which the latch dogs 55 normally extend so as to expose teeth 58, except when the core barrel is being retracted. The

lower ends 70 of slots 59 are tapered inwardly for engagement with the outer sloping edges of the latch dogsV 55 and upon upward movement of the latch retracting case 66, the latch dogs 55 aremoved inwardly so as to bring teeth portions 58 out of engagement with the latching hold down shoulder 60 on locking coupling 61. The periphery of the latch retracting case 66 is also provided with two other slots 71 the plane of the axes of which is perpendicular to the plane of the axes of the tirst slots 59 and the slots 71 are positioned lower down on the latch retracting case 66 for receiving the ends of pin 57 which pivotally mounts the latch dogs S5 in the latch body. The pin 57 and slots 71 limit the sliding movement of latch retracting case 66 relative to latch body 44. A threaded spear head 72 is screwed into the top of the latch retracting case 66 and is held against loosening by a set screw 74 in a set screw socket 75 in the side of the latch retracting case 66.

Guide coupling 62 which encloses the latching mechanism is threaded (at its lower end) into hanger coupling 26 and is provided on its outer surfaces with a plurality of strips or ribs 76 of Stellite or similar hard metal facing material to guide the thickened lower end of the drill stem.v

and to prevent wobbling thereof.

The lower end of locking coupling 61 is threaded jinto guide coupling 62 and the upper end of the coupling is threaded for receiving `the lowermost section 77 of the Y Conventional drill rod forming drill stem 10. The lower end of locking coupling 61 is cut away over slightly more than one half of its diameter from 78 to 79 (as shown in Figures 4 and 5) for engagement with the sides of the latch dogs to impart the rotary movement of the drill string to the latch body 44. This serves to key latch body 44 to the drill stem, and parts thereof, particularly shoulders 24 and 25, are kept from wearing. It may be noted that surface 60, upon which teeth 58 of latch dogs 55 seat, is a part of this cut-away portion between 73 and 79 The grappling tool or overshot assembly is indicated generally at 80 in place in the drill stem and in a ready position for retracting the core barrel inner tube assembly 20. The overshot assembly 80 includes a pair of pulling dogs 81 the jaws S2 of which are shown grasping the Spearhead 72 of theV core barrel assembly. The pulling dogs 81 are disposed in a face-to-face position in an elongated transverse slot 85 in the overshot body 84 and are pivotally mounted on a pin 86 extending through the overshot body andthrough the partially cut away and overlapping hubportions 87 of the pulling dogs. A coil compression spring 88, which is seated upon pins 89 welded to the upper ends of the pulling dogs, normally urges these ends apart and thus normally urges the jaws 82 together in grasping position while permitting expansion of the jaws to slide over the top of the spear head 72 when theovershot assembly is lowered through the drill stem. The lower end portion of the overshot body, below the slot containing the pulling dogs, forms a collar 90 which lits down over a corresponding cylindrical projection forming the top V69 of the latch retracting case and imparts stability to the entire assembly 20 in respect to the overshot assembly 80 as they are both withdrawn from the well. Normally, in prior art devices without this collar, the

core barrel .assembly is free to l swing #pivotally -from Y the.

. at the bottom of the well, or upon the drill platform with danger of injury to operators and equipment.

The upper end 92 of the overshot body is internally screw threaded for coupling .with a companion lower jar element 94 which has a central aperture 95 into which one end of a rod 96 is fitted and is heldin place by a pin 97l extending through the lower jar element and the rod. Fitted over the upper end of rod 96 is an externally threaded upper jar element 98.A The top of rod 96 is threaded and a nut 99 is locked in place at the top end of the rod. The upper jar element 98 is coupled into the lower end of a section of tube 100 and a wire coupling element 101 having a central aperture 102 serves as an attachment for wire line or cable 104 which may be passed thru member 101 and knotted or otherwise fastened.

The upper jarring elements 101-100--98 permit of a hammering action against the lower jar element 94 and the overshot body 84 when such action becomes necessary to force the jaws 82 of the pulling dogs 81 over the Spearhead 72 of the core barrel. The hammering action may be achieved simply by lifting the wire line permitting the upper jar element to slide up the length of rod 96 and then dropping, whereby the lower face of the upper jar element 98 hammers upon the upper face of the lower jar element 94. This action is also eifective for delivering a sharp blow to the latch body 44 of ing the dogs 55. Upward jarring will move the latch retracting case 66 and will serve to free teeth 58 of dogs 55 from shoulder 60 in the event they are stuck, as can happen occasionally. The jarring action thru wire line manipulation thus` gives the driller a new facility of operation.

ln the oper-ation of the core taking apparatus which hole being drilled. The elongatedtubular sections which make up the drill stem 10 extend to the earths surface. Part of the hole above the drill bit may be provided with a casing. The upper section of the drill stem is suitably held at the surface for rotation and advancement by conventional drilling equipment. It is customary to introduce a drilling fluid or mud the tubular drill stem and continuously circulate such fluid through the hole, the liquid serving to lubricate and assist the drill bit in cutting and to carry the particles cut from the earths formations up around the outside of the drilll stem tothe surface Where the cuttings are allowedto settle out and the uid is recirculated. The core barrel inner tube assembly 20 may be lowered down through the drill stem by means of wire line, or it may be dropped by gravity to the bottom of the drill stem. The presence of drilling uid within the drill stem serves to restrict the velocity of a freely falling core barrel inner tube assembly 420 through the tubing, and in use of our invention we prefer simply to drop the emptied assembly thru the drill stem. It will fall thru the water or other drill iluid at a rate which is not excessive, and will come to rest with shoulders 24-25 in contact. The

walls of the drill tubing 10 urge the normally outwardly extending latch dogs 55 inwardly Vagainst their springs f nular shoulder 25 on the inner periphery of the hanger v coupling 26. Normally,

this section of shoulder upon shoulder would act as a the core barrel freedown into the interior of i valve and cutoff the ow andf circulation of the drilling but arcuatecliannelshSQ asass" t cut into the llatch body of the core barrel permit flow of the drilling fluid around the shoulder supporting means. The shoulder 24 of the latch body of the` core 'barrel rests upon the shoulder 25 of the drill stem so as to support the core lifter case 30 at the end of the inner core-receiving tube 27 out of contact with the inner shoulder' 17 of the bit 11 and hence s'erves to protect the end of the core receiving tubes 27-28-30 from damage and therefore protects the core sample from damage resulting therefrom.

As the shoulder 25 of the latch body 44 comes to rest upon the shoulder 24 of the drill stem the latch dogs 55 snap outwardly into their normal open position and engage locking coupling 61, the upper edges of the dogs seating under the locking coupling so as to prevent the core barrel from moving upward through the drill stem as the core is being cut. The sides of the latch dogs 55 engage the cut away section 78-79 of the locking coupling and lock the latch body for rotation with the drill stem. Latch dog springs 64 hold the latch dogs in locked position during the cutting of the core sample.

The core barrel inner tube assembly is now ready to receive the core sample. Rotation of the drill string may now be started and the cutting of the core begun. Because of the annular shape of the cutting surfaces 12-14 and the central aperture 18 of the drill bit 11 the drilling action forms an ever deepening circular hole with a rigid rodlike shaft or core of the strata being cut being forced -up through the central aperture 18 of the drill bit, through the core lifter case 30 and core lifter ring 29 into the core receiving tube 27. Because of thel locked position of the latch dogs 55 the upper sections of the core barrel inner tube assembly 20, namely Ithe latch body 44 and associated parts, rotate with the rotation of the drill stem 10. However, because of the antifriction bearing structure 47-48 between the latch body 44 and the inner tube cap 32.the core receiving tube 27 (and associated parts 28, 30, 31, and 32), being freely rotatable with respect tothe drill stem 10, may remain stationary while the drill stem rotates. Thus the core sample itself is not subject to damage as a result of the tube 27 (and associated parts), rotating around it. As the core sample rises upwardly into the core-receiving tube 27 any drilling mud or other well uids trapped within the inner tube are forced out and permitted to escape through the ports 34 adjacent the top of the inner tube.

After the core of the desired length has been cut the drilling is stopped and the water coupling removed from the surface end of the drill stem 10. Then the drill stem is pulled upward a short distance to break the core, and the overshot assembly 80 is lowered into the hole at the end of a Wire line 104. Upon arrival of assembly 80 at the top of the core barrel inner tube assembly 20, the jaws 82 of the pulling dogs 81 snap down over the Spearhead 72 at the top of the latch retracting case 6,6 and the stabilizing collar 90 ts down over the top 69 of the case. If any resistance is encountered, the wire line is lifted and dropped to deliver a sharp drop hammer blow to the core barrel inner tube assembly 20 by lifting the upper jar element 98 of the overshot which is attached to the Wire line, sliding it up the length of rod 96 and then dropping it. One sharp blow delivered as the upper jar element 98 strikes against the lower jar element 94 is usually suicient to make the coupling. If not, the procedure may be repeated. If the dogs 55 do'not come free by a simple pull of wire line 104, they may be hammered loose by lowering line 104 and quickly raising it to strike end 98 against head 99, Y

Tension is then put upon thev wire line 104 (as with a conventional winch or other suitable hoist) to withdraw the core barrel inner tube assembly 20 upwardly through thevdrill stem.v As the pulling dogs 81 of the overshotassembly pull upward upon the Spearhead' 72 on the'la't'ch retracting case 66 the tapered slots 70 of the retracting pin 97 in the overshot assembly will shear ot removing4 the danger of the wire line breaking in an attempt to force the core barrel. In such case, the wire line is withdrawn and the drill string 10 is recovered, according to conventional practice for recovering the core.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments herein.

What we claim is:

l. In a rotary drill apparatus for taking core samples, a tubular drill stem, a core bit having minimum and maximum diameters atached to the end of the drill stem for boring Van annular opening into earth formation thereby to provide a core sample having substantially the minimum diameter of the bit, said drill stem having at a position adjacent but spaced from the bit an internal suspension shoulder forming a portion of minimum diameter of the drill stem, a core barrel inner tube assembly of a size throughout most of its length such that it can pass axially through the tubular drill stem and through said portion of minimum diameter at said suspension shoulder and provide space for fluid to flow between said assembly and said drill stem, said core barrel inner tube assembly having thereon an external shoulder of a size such that it will rest cooperatively upon the internal suspension shoulder of the drill stern and thereby position the core barrel inner tube assembly with the end thereof closely adjacent but spaced over the minimum diameter portion of the bit, said core barrel inner tube assembly including an open ended tube facing the bit, said tube having an internal diameter suficiently large` to receive the core, a core lifter mounted in the apparatus adjacent said bit for engaging and holding core in said open ended tube, said apparatus being provided with channels at said shoulders for conducting a flow of iluid from the drill stem, thence through the channels at said shoulders and thence between the drill stem and core barrel inner tube assembly and thence through said portion of minimum diameter and thence radially outwardly across the face of said bit, retractable latch means on said assembly and cooperating internal detent shoulder means on the drill stem to prevent movement of the assembly away from the bit until the latch is withdrawn, and latch actuating means forming part of said assembly movable relative thereto for engaging the latch means to move it to unlatching position.

2. In a rotary drill apparatus for taking core samples, a tubular drill stem, a core bit having a central axial aperture at the end of said drill stem, a retractable core barrel assembly positioned within said tubular drill stem adjacent said bit, open ended tube means on said assembly for receiving and holding a core sample, complementary shoulder means on said core barrel assembly and within said drill stem for supporting the end of the open end of said core barrel tube out of contact with the inner portion of said bit, said apparatus being provided with channels at said shoulder means, and the external diameter of said core barrel assembly relative the internal diameter of said drill stem above and below said shoulder means being such as to provide an uninterrupted space for Huid ow from the tubular drill stem, thence past said shoulder means and between said core barrel tube and drill stem, thence through the space between the open end of said core barrel tube and the adjacent inner portion of said bit and thence radially outwardly yacross the face of the bit, retractable latch means on the core barrelassembly andrlatch engaging rests on the apparatus against which the latches engage for holding said core barrel assembly in place with said shoulder means in engagement and movable means on the assembly for engaging said latch means for positively moving such latch means out of engagement with said rests.

3. In a rotary core drilling apparatus for taking core samples, an elongated tubular drill stem, a core bit having an outer diameter and an inner diameter defining a central axial core forming and receiving aperture, said bit being mounted on the drill stem for rotation therewith, a retractable core barrel assembly including an elongated core receiving tube positioned coaxially Within the drill stem and having an open end adapted to receive core as produced by said bit; means mounted on the apparatus adjacent the bit `for Yholding a core sample within said core barrel tube, complementary first and second shoulders on the apparatus, the first shoulder being on the inside of the tubular drill stem and having a seat directed away from the bit and the second shoulder being on the core barrel assembly, and having a seat directed toward the bit and shaped to engage the first shoulder and hold the open end of the core barrel tube of said core barrel assembly in spaced relation but close to the bit, said apparatus being provided with channels for conducting fluid from said drill stem thence past said shoulders when they are engaged, the interior diameter of the drill stem being larger than the exterior diameter of the core barrel tube so as to provide an annular space for fluid to pass unobstructedly therethrough to the inner diameter portion of said bit and thence radially outwardly across the bit face, the interior surface of said drill stem being formed with a latch rest adjacent the shoulder on said drill stern, a latch dog mounted on the core barrel assembly for movement into and out of engagement with said rest when the shoulders of the drill stem and core barrel are engaged, and actuating means forming a part ofthe core barrel assembly positioned to engage said latch dog and positively move it out of engagement with said rest, said actuating means being engageable by a grapple lowered through the drill stem.

4. The rotary core drilling apparatus of claim 3 further characterized in that the outer diameter of said bit is about twice as much as the inner diameter of said bit.

5. The rotary core drilling apparatus of claim 3 further characterized in that the shoulder on the drill stem is an interior flange forming an aperture slightly larger than the core barrel tube which passes therethrough and said core barrel assembly shoulder is an exterior flange which is adapted to rest on the drill stem flange.

6. The rotary core drilling apparatus of claim 3 further characterized in that the latch dog is pivoted thereon for swinging movement of a surface thereof into and out of engagement with said latch rest and said actuating means ,is a tubular member slidably mounted for limited movement and includes a wedge surface for engaging said latch dog for moving it out of engagement with said rest. p 7. The rotary core drilling apparatus of claim 3 further characterized in that the drill stem is provided with a surface for engaging a part of the core barrel assembly for rotating said part with the stem when the latch dog is engaged in said latch rest.

8. The rotary core drilling apparatus of claim 3 further characterized in that that portion of the core barrel assembly which includes the shoulder is provided with a journal and said core barrel tube is mounted thereon for rotation coaxially in respect to the drill stem.

9. A rotary drilling apparatus for taking samples of subsurface formations comprising a sectionalized drill stem terminating in an annular diamond drill bit having an outer diameter slightly larger than the outer diameter of the drill stem for forming the hole and an inner diameter forming the core, said drill stem being tubular and providing a clear unobstructed space therein the diameter of which is larger than the core, a ,portion of said stem including an inwardly extending shoulder of a diameter slightly less than the diameter ofthe unobstructed space in said drill stem, a core barrel inner tube assembly of generally elongated cylindrical shape having an external diameter larger than the inner diameter of the bit but sufficiently less than the inner diameter of the drill stem so as to permit passage of fluid between the assembly and the drill stem, said assembly being enlarged at Vone place along its length so as to form a flange thereon, said flange being of a size such that it passes without obstruction through the clear unobstructed space of the drill stem but sufficiently large so as to engage the shoulder of the drill stem and be supported thereon, said assembly including an open ended core receiving tube of a length and so positioned that' said end of the tube will be positioned close to but spaced over the bit adjacent the inner diameter thereof when the flange of the assembly is seated on the shoulder of the drill stem, said apparatus including passageways at said shoulder and flange when they are engaged so as to permit the Vpassage of fluid from the drill stem thence through the passageways and through the passageways and through the space between the assembly and drill stem and to the inner diameter of the bit and thence radially outwardly across the face of the bit, latch dog means mounted for movement in respect to the assembly from a retracted position within the cylindrical dimensional confines of the assembly to an extended position beyond said assembly, said drill stem including a latch dog seat positioned and oriented so that said latch dog means can bear against said seat and restrain movement of said assembly away from the bit when the assembly flange is engaged on said drill stem shoulder, and release means on the assembly mounted for limited axial movement relative thereto for engaging and retracting said latch dog means out of engagement with said seat when said release means is moved axially away from said bit, said release means including a grapple coupling.

10. In a retractable wire line core barrel inner tube assembly for a core drill, which assembly is adapted to be lowered through a drill stem and supported in working position by engagement of a complementary seat on the assembly upon a cooperative seat on the stem, the im` provement comprising a cylindrical latch body having an upper end and a lower end, a cylindrical core-receiving tube journaled co-axially on the lower end of said latch body so as to be suspended therefrom, said latch body having an elongated closed-end slot entirely therethru, a pair of elongated latch dogs in the form of lat bars placed side-by-side in said slot and substantially filling said slot, a common pivot pin thru the body and latch dogs at the lower end of said slot and latch dogs, mounting the latch dogs in a generally axial position in repect to and as a part of the assembly for swinging movement of the upper ends of the latch dogs from a retracted position in which both latch dogs are entirely contained within the slot and within the dimensional confines of the cylindrical latch body, to a position in which the upper ends of the dogs swing respectively in opposite directions from said slot for engaging the upper exterior corners thereof against a seat on the drill stem, and in which latter position each of the latch dogs has its upper exterior corner outwardly disposed in respect to the slot, each of said latch dog bars being shaped so as each to have an outer edge surface extending from said upper exterior corner and thence downwardly toward the .axis of the drill stem, means normally biasing the latch dogs outwardly, a cylindrical sleeve forming a part of said assembly, said sleeve being slidable endways in respect to the cylindrical latch body and in respect to the latch dogs of the assembly, said sleeve having oppositely disposed longitudinal slots therein so located that the corners of the latch dogs can swing outwardly therethrough, said sleeve being provided with stop surface for limiting the ei-idwise slidable motion 'thereof relative to saidlatch dog, an. end of each of the slots in said sleeve being engageable respectively on edge surfaces of one of the latch dogs as the sleeve is moved endwise for positively swinging the latch dogs into retracted position in said slot, said sleeve having on the upper end thereof in respect to the latch body, a coupling shaped so as to be engageable by a grapple.

l1. The apparatus of claim 10 further characterized in that the pin extending transversely through the slot upon which the latch dogs are pivotedis extended so that at least one end thereof terminates beyond the latch body and said sleeve is provided with another slot in which said end of the pin is positioned, said pin thereby References Citedin the file of this patent i UNITED STATES PATENTS Otis Feb. 21, Barrett et al. Nov. 12, Oliver Mar. 16, Church May 18, Sherman Aug. 23, Noble Dec. 26, Copelin Feb. 6, Mitchell July 1, Brown May 8, Williams May 10, 

